The present invention relates to a winch.
German patent specification DE-AS 1, 481,878 describes a pneumatically operated hoist with automatic weight compensation, including a housing which bounds a working pressure chamber of variable volume. The working chamber is demarcated on one side by a piston which travels longitudinally in the working chamber and forms in conjunction with a spindle and a spindle nut a drive unit for a rope drum. The spindle is guided in longitudinal direction by the spindle nut which is securely fixed to the housing. One end of the spindle is connected to the rope drum in a fixed rotative engagement, with the spindle and the rope drum being disposed in coaxial relationship. Operation of the rope drum is realized through a build-up of gas pressure in the working chamber so that the piston is pushed against an end face of the rope drum, thereby displacing the rope drum along the spindle and as a consequence causing a conjoint rotation of the spindle and the rope drum. A rotation of the piston as a result of the rotational movement of the rope drum is prevented by a coaxial disposition of a pivot bearing between the piston and the rope drum. The pivot bearing includes two bearing rings in side-by-side disposition in direction of the rotation axis, wherein during operation, one bearing ring rests on the end face of the rope drum and the other bearing ring rests on the piston.
This conventional hoist suffers the drawback that during transport of the hoist or at pressure drop during operation, i.e. when no gas pressure is encountered in the working chamber, the piston tilts in the pressure chamber. As a consequence, the sealing action is compromised so that the winch becomes useless. This defect can only be rectified through dismantling of the hoist.